Archive for the ‘Entomology’ category

Its very easy for army officers to assume that journeying cross-country is simple. They forget that they are specially trained (in map-reading), specially equipped (with compass, GPS and maps) and there is a huge infrastructure ( of cartographers, satellites, high-quality printing presses, logistics, people to update) behind them!

Butterflies dont need compasses or maps...

Compare this with a butterfly? What could be the limits of its vision? How can it find its way across continents which are proportionally about a few hundred to thousand times larger? Without consciousness how do they do what they do?

And the only instrument they have for navigation is the sun in the sky!

...or GPS to help them migrate over areas they have never travelled before!

Take the Monarch, for instance! This Danaid or Milkweed-family butterfly is universally known for its migration which has been well-documented and researched for over a hundred years. The state butterfly or state insect for eight American states, it is the most popular butterfly in North America.

Here’s a very nice look at the place the Monarch butterfly holds in the hearts of the American people!

The Monarch (Danaus plexippus), a relative of India's Common and Plain Tigers, is a well-known migrant.

Wikipedia tells us about the Monarch’s migration that… :-

In North America, Monarch butterflies make massive southward migrations starting in August until the first frost. The northward return migration takes place in the spring. The monarch is the only butterfly that migrates both north and south as the birds do on a regular basis. But no single individual makes the entire round trip. Female monarchs deposit eggs for the next generation during these migrations.

Take the case of the population east of the Rocky Mountains. By the end of October, this population migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve in the Mexican states of Michoacán and México (the western population overwinters elsewhere).

The length of these journeys exceeds the normal lifespan of most monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a non-reproductive phase known as diapause and may live seven months or more which enables it to migrate from the United States and over-winter in Mexico.

The generation that overwinters generally does not reproduce until it leaves the overwintering site sometime in February and March. It is thought that the overwinter population of those east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration. It is the second, third and fourth generations that return to their northern locations in the United States and Canada in the spring.

Now, how can a Monarch keep heading South throughout the day when the sun shifts its position from low on the horizon to its highest point at mid-day and again low in the evening?

As the Sun moves across the sky during the day, the Monarch must continuously adjust its calculations so that it does not waver from its chosen direction – South!.

Scientists have now found the key to the Monarch’s genius. It’s in the antennae!

The antennae of the Monarch play a vital role in navigtion during migration.

Researchers at the University of Massachusetts Medical School held the butterfly wings gently and dipped their antennas in enamel paint. They painted the antennas of one set of Monarch butterflies with black paint (which blocked both light and smell) and the antennas of another set were painted with clear paint (which blocked smell but permitted light).

The Monarchs with clear-painted antennas found their way around while those whose antennas were painted black-painted got lost!

That not only showed the antennas were sensing light for navigating, it also showed that the sense of smell isn’t involved in finding the way, since both paints blocked that ability.

And, since the animals with black paint got lost even though their eyes were able to see light, the researchers concluded the antennas were vital to finding the way.

Butterflies whose antennas were surgically removed also became disoriented.

Now how does this work?

In 2008, scientists of of the University of Massachusetts Medical School discovered that Monarchs have ancestral circadian clock mechanisms in their brain which tell them the relative time of the day. This circadian rhythm is formed by the production of and complex biochemical interaction of cryptochrome proteins, which act as critical components in the circadian clock mechanism. Two cryptochrome proteins, named Cry1 and Cry2 were also thought to connect the clock to the sun compass somehow for successful navigation.

This year, the new ‘antenna-painting’ study by this team proved that this sun compass was located in the antenna. Apparently, the antenna sun-compass gives Monarchs the ability to detect the position of the sun and the direction of polarized light.

Gif showing the great wanderings of the Monarch generations! (click to see the gif in action)

When this information is combined with time information from the circadian clock, monarchs are able to steer a course to the South each day and eventually to find their way from all over North America to the Mexican highlands, where they spend the winter.